2978 - Feasibility and Stability of Surface-Guided Deep Inspiration Breath-Hold for Mediastinal Radiotherapy: A CBCT-Based Analysis

12:30pm - 01:45pm ET

Poster Hall - Exhibit Hall A

Screen: 11

POSTER

Presenter(s)

Zhen Cui, RT, MBBS - Shandong Cancer Hospital and Institute, Jinan, Shandong

Z. Cui¹, X. Li¹, and Z. Li²; ¹Department of Radiation Oncology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, Shandong, China, ²Department of Radiation Oncology Physics and Technology, Shandong Cancer Hospital and Institute, Shandong First Medical University and Shandong Academy of Medical Sciences, Jinan, China

Purpose/Objective(s):

To compare setup accuracy between free breathing (FB) and surface guided deep inspiration breath-hold (SG-DIBH) using cone-beam CT (CBCT) for mediastinal radiotherapy, evaluate the feasibility of the technique, derive planning target volume (PTV) margins using van Herk formula, and assess intra-fractional stability of SG-DIBH using post-treatment CBCT in SG-DIBH cohort.

Materials/Methods:

Pre-treatment CBCT translational shifts in translational directions: vertical (Vrt), longitudinal (Lng), lateral (Lat), and rotational directions: pitch, roll and yaw were retrospectively analysed for patients treated under FB and SG-DIBH conditions. SG-DIBH treatments were performed using a surface-guided radiotherapy system (AlignRT®, Vision RT Ltd.) for real-time patient positioning, breath-hold monitoring, and intra-fraction motion management. Signed mean shifts and standard deviations were derived, and PTV margins were calculated using the van Herk formula (2.5S + 0.7s). For SG-DIBH patients, post-treatment CBCTs acquired were analysed to evaluate intra-fractional stability and breath-hold reproducibility. As all pre-treatment CBCT shifts have been applied, residual shifts observed on post-treatment CBCTs represent intra-fractional positioning error.

Results:

Compared with FB, SG-DIBH demonstrated improved setup accuracy with reduced variability in all translational directions. Calculated PTV margins for FB were 0.83cm (Vrt), 1.03cm (Lng), and 0.48cm (Lat), whereas corresponding SG-DIBH margins were reduced to 0.40 cm (Vrt), 0.35 cm (Lng), and 0.37 cm (Lat). Analysis of post-treatment CBCTs showed minimal intra-fractional displacement during SG-DIBH: median absolute translational shifts were 0.08cm (Vrt), 0.15cm (Lng), 0.06 (Lat), of 1.0° (pitch), 0.5° (roll) and 0.4°(yaw) with acceptable to narrow IQR of slightly above 1mm and 0.5°. These findings indicate minimal patient drift during beam delivery and confirm that SG-DIBH position was stable throughout treatment.

Conclusion:

Mediastinal SG-DIBH using AlignRT is a feasible and geometrically stable treatment technique, offering improved setup accuracy compared with FB and enabling substantially reduced PTV margins when calculated using the van Herk approach. Post-treatment CBCT analysis confirms excellent intra-fractional stability of SG-DIBH, supporting its clinical implementation for mediastinal radiotherapy where motion management and margin reduction are critical.